It was once believed that the flesh of the peacock never corrupts, so peacocks became the classic symbol of immortality. They are an ancient Christian symbol of the Resurrection, and representations of them are found on the tombs of ancient Christians as an expression of their hope to follow Christ in His defeat of death.

Bells are another lovely symbol for the day as they are said to have gone to Rome on Maundy Thursday only to have started returning home at last evening's Easter Vigil to ring joyfully (in France and Belgium, it is these bells, not the Easter bunny, that bring the Easter eggs -- see below).

In the United States, the most common symbol of that glorious resurrection for the entire Easter Season is the lily (lilium longiflorum). Jesus loved lilies!:

Luke 12:27
Consider the lilies, how they grow: they labour not, neither do they spin. But I say to you, not even Solomon in all his glory was clothed like one of these.
The lily represents purity, chastity, innocence, and St. Gabriel's trumpet, and is a symbol of Our Lady and used to depict the purity of the Saints, especially SS. Joseph, Francis, Clare, Anthony of Padua, and Catherine of Siena. In America, it has become, too, a symbol of the Resurrection. Legend says that lilies originated with Eve's tears when the first couple was banished from the Garden of Eden. Other legend says that they sprang up from the ground when drops of blood fell to the foot of the Cross. It is interesting that these two legends exist, because Christ, the New Adam, wipes away the tears of the children of Eve who became the children of Mary when Christ gave her to us, through John, from the Cross. Mary herself is symbolized also by another lily, lilium candidum, or the Madonna Lily (or "Annunciation Lily").2

Butterflies, too, are an apt symbol of the day's meaning. Beginning life as lowly humble caterpillars, they "entomb" themselves in cocoons only to emerge with jewel-colored wings and the ability to soar. What better symbol of the Resurrection -- except maybe for eggs, which had always been symbols of Spring and were items of wonderment to all -- an inanimate object out of which comes life. For Christians, they became the perfect symbol of the tomb Christ conquered, and Jews used (and used) them on their Passover, too, as the Haggadot specifically calls for it as a symbol of rebirth (this is a rabbinical command, not a Scriptural one). 3

Another level of symbolism is that the egg represents birth, the Creation, the elements, and the world itself, with the shell representing the firmament, the vault of the sky where the fiery stars lie; the thin membrane symbolizing air; the white symbolizing the waters; and the yolk representing earth. Painted red, eggs are a demonstration that the salvation and re-birth of the world comes through Christ's Blood and Resurrection. Old legend has it that St. Mary Magdalen went to Rome and met with the Emperor Tiberius to tell him about the Resurrection of Jesus. She held out an egg to him as a symbol of this, and he scoffed, saying that a man could no more rise from the dead than that egg that she held could turn scarlet. The egg turned deep red in her hands, and this is the origin of Easter eggs, and the reason why Mary Magdalen is often portrayed holding a scarlet egg.